In the 1662 prayer book there are several fasts appointed on the eve, or vigil, or day before several of the holy days in the church year. Curiously, not all of the holy days in that prayer book get their own fast day beforehand; perhaps about 75% do and the rest do not.
Today is one such vigil fast, preparing us for the feast of the nativity of Saint John the Baptist tomorrow! This pairing of fasts and feasts is both an ancient and a sound practice:
Here, the great Anglican theologian, Richard Hooker, points out that grief and joy are two states of heart and mind which excellently summarize human life, and in her fast and feast days the church uses grief and joy to help Christians grow in virtue and holiness.
So if you are not normally one who observes days of fasting consider adopting the prayer book tradition of vigil fasts today!